1) Field of the Invention
The present invention relates to fuel systems for internal combustion engines and more particularly to fuel systems that provide both primary fuel and alternate fuel to an internal combustion engine.
2) Description of Related Art
For a variety of reasons, most of which relate to environmental and alternative energy pursuits, certain primary fuel engines, such as diesel engines, can be made to accommodate alternate fuels, such as straight vegetable oil (SVO), “biodiesel,” and other fuel oils (hereinafter “alternate fuels”). However, practical applications have demonstrated that full-time use of these alternate fuels is not desirable. For instance, at low temperatures the viscosity of some of these alternate fuels is not optimal for use in an engine designed to run on primary fuel. The alternate fuel should be heated up to a temperature that will allow it to easily pass through the fuel delivery system. If left in an idle engine to cool, the alternate fuel also has a tendency to increase in viscosity and thus congeal inside the fuel delivery components. Thus, the alternate fuel should not be used until it has reached an appropriate temperature and it should be purged from the engine before shutting down. As a result, some of these systems typically run on diesel fuel during start-up and before shut down, and rely on the consumer to manually switch to the alternate fuel source in between, i.e., when the alternate fuel is at an optimal temperature. For example, in an automobile that has been modified to include diesel and alternative fuel tanks, a driver can selectively toggle between the two fuels during operation of the vehicle using a switch that controls the flow of the two fuels.
Recently, some aftermarket automated control systems have been designed. These systems control the switching between a diesel fuel source and an alternative fuel source based on the temperature of the alternate fuel. Typically, when the engine is cold, such as during engine start, the engine operates using primary fuel, and once a predetermined alternate fuel temperature or a certain vehicle speed is achieved, the engine is then switched to the alternate fuel. If low temperature operation reoccurs, the engine is then switched back to primary fuel, and so on.
To automate this fuel selection process, various conventional aftermarket control systems have been designed that acquire and monitor alternate fuel temperature by using various measurement devices, such as temperature sensors. However, these aftermarket systems are constrained in that they relate switching between the two fuel sources based directly on the temperature of the alternate fuel. Furthermore, conventional control systems that switch between primary fuel and alternate fuel use either 100% primary fuel or 100% alternate fuel at all times, even though neither fuel may be optimal during some operating conditions. This abrupt switching of fuels can result in abrupt changes in engine behavior. Reduced or unacceptable performance may be experienced at or near the switching transition point, and potential utilization of alternate fuel may be forfeited during intermediate conditions by forcing premature switching of fuel to mitigate transition behavior. As a result, conventional alternate fuel systems typically suffer from difficulty in integration, do not accommodate grade loading, exhibit poor performance at fuel type transition points, must underutilize alternate fuel, and are not applicable to engine types intolerable of 100% alternate fuel mixtures.
Therefore, an improved system and method of automatically supplying an internal combustion engine with a primary fuel, an alternate fuel, or a combination of both, based on a variety of operating conditions are desired.